KR20120056952A - Method for MICRO-STEPPING VARIABLE STRUCTURE CONROL OF PERMANENT MAGNET STEP MOTOR - Google Patents

Abstract

PURPOSE: A method for controlling a micro stepping variable structure of a permanent magnet step motor is provided to improve location following performance of a step motor by compensating an error due to counter electro-motive force and phase delay. CONSTITUTION: A desire voltage or a desire current is obtained for driving a step motor is obtained by using a desire position of a rotator in regard to a stator(1100). A voltage error or a current error is used for maintaining the desire current or a current according to the desire voltage(1200). Counter electro-motive force of the step motor is estimated by using a disturbance observer(1300). An actual input voltage is obtained by using the estimated counter electro-motive force and the voltage error(1400). The actual input voltage is applied to the step motor(1500).

Description

METHOD FOR MICRO-STEPPING VARIABLE STRUCTURE CONROL OF PERMANENT MAGNET STEP MOTOR}

The present invention relates to a microstepping variable structure control method for a permanent magnet step motor, and more particularly to a microstepping variable structure control method for a permanent magnet step motor capable of compensating for errors due to back EMF and phase delay.

In general, step motors (or stepping motors or stepper motors) are widely used in applications requiring precise position control, such as robotic positioning systems. Step motors are the motors most commonly used for general position control at present, and can be said to be suitable motors where position stop accuracy is required. In case of stepper motor, the position control structure has open loop control and rotates based on the mechanical step angle of the stepper motor, so the current rotation is based on the step angle input to the stepper motor. It is easy to control because the position can be determined, so the application cost is low. When the step motor is transferred to the correct position, no further control for position movement is made. It is widely used in demanding semiconductor equipment.

Step motors are electrically classified into two phase step motors and five phase step motors. This refers to the number of phases of the power supplied to the stepper motor, which is equivalent to categorizing the induction motor into an electrically single phase induction motor or a polyphase (three phase) induction motor. Therefore, the two-phase step motor is configured to rotate by 1.8 degrees with respect to one pulse of the input pulse, and has a rotation angle of 200 steps per revolution, and the five-phase step motor has a step angle of 0.72 degrees. Have

Using a suitable controller, most step motors can be driven in half-steps, and some controllers can drive step motors in smaller steps or micro steps.

On the other hand, the stepper motor can be driven by an open loop control system and can maintain stability at any step position because it provides precise position control within an integer step without a position sensor. In other words, no feedback is required for control.

However, the open loop control has a problem of poor performance due to excessive overshoot, oscillatory response and long settling time. And, due to this problem, the stepper motor cannot be used without a feedback sensor, and high performance closed loop control that requires accurate positioning cannot be used.

In order to control the stepper motor, a current PI (proportional integral) controller is used. When only the current PI controller is used, a problem occurs due to back-emf or phase lag.

That is, there is a problem that the phase current decreases due to the back EMF and the phase delay. As the speed of the step motor increases, the current decreases due to the back-EMF and phase lag of the step motor.

The present invention provides a microstepping variable structure control method for a permanent magnet stepper motor capable of compensating for a decrease in current due to counter electromotive force and phase delay.

The present invention provides a microstepping variable structure control method of a permanent magnet step motor having excellent position control performance.

One embodiment of the present invention for achieving the above object, in the microstepping variable structure control method of a permanent magnet step motor having a stator and a rotor, using the desired position of the rotor with respect to the stator Obtaining a desired voltage or a desired current for driving the step motor; Using a voltage error or a current error to maintain a current according to the desired voltage or the desired current; Estimating counter electromotive force of the step motor using the disturbance observer; Obtaining an actual input voltage using the voltage error and the estimated back electromotive force; And applying the actual input voltage to the step motor. The counter electromotive force and phase delay may be simultaneously removed.

The step of using the voltage error or current error is obtained from the difference between the product of the desired voltage and the input current of the permanent magnet step motor and the resistance of the coil wound on the stator, or the current error is the desired current and the permanent It can be obtained from the difference of the input current of the magnet step motor.

In the estimating counter electromotive force, the disturbance observer may be in the form of a high pass filter.

The obtaining of the actual input voltage may include variable structure control of the voltage error and the estimated back electromotive force.

The desired voltage or the desired current is characterized by a sinusoidal function of the maximum voltage or the maximum current.

The winding resistance value of the step motor is characterized by using the same value as the value provided in the step motor data, or by actual measurement or adaptive control (adaptive control).

As described above, the microstepping variable structure control method of the permanent magnet step motor according to the present invention can compensate for the current decrease and the phase delay caused by the counter electromotive force in the current loop.

The microstepping variable structure control method of the permanent magnet step motor according to the present invention can improve the position tracking performance of the stepper motor by compensating for errors caused by back EMF and phase delay.

The microstepping variable structure control method of a permanent magnet stepper motor according to the present invention improves the microstepping performance of a stepper motor by estimating back EMF using a disturbance observer and compensating back EMF and phase delay using a variable structure control (VSC). It is possible to implement a control robust to back EMF.

In addition, since the microstepping variable structure control method of the permanent magnet stepper motor according to the present invention requires only current feedback, the configuration of the control system can be simplified, and the position tracking can be performed rather than the microstepping using only the current PI feedback. It can improve performance.

1 is a partially cutaway perspective view showing a step motor according to an embodiment of the present invention.
FIG. 2 is a block diagram for controlling the permanent magnet step motor according to FIG. 1.
3 is a flowchart illustrating a method for controlling a microstepping variable structure of a permanent magnet step motor according to an exemplary embodiment of the present invention.
4 to 6 are experimental data graphs showing the performance of the step motor according to the variable structure control method of the permanent magnet step motor according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the embodiments. Like reference numerals in the drawings denote like elements.

1 is a partial cutaway perspective view showing a step motor according to an embodiment of the present invention, Figure 2 is a block diagram for controlling a permanent magnet step motor according to Figure 1, Figure 3 is an embodiment of the present invention Flow chart illustrating a method for controlling a microstepping variable structure of a permanent magnet step motor according to an example. FIGS. 4 to 6 are graphs of experimental data showing the performance of a step motor according to the variable structure control method of a permanent magnet step motor according to the present invention. to be.

As shown in FIG. 1, the step motor 100 according to the exemplary embodiment of the present invention comprises a rotor 140 installed inside the case 110 as a permanent magnet to wound the stator 130. It is configured to react with the magnetic flux generated by the current applied in the coil. The stator 130 is a slotted stator, and two windings of the stator 130 are positioned to have two phases. Rotor 140 made of a permanent magnet is installed on the rotating shaft 120 to rotate with the rotating shaft 120, and has an N pole and an S pole. In this way, the internal rotor 140 is composed of a permanent magnet is called a permanent magnet stepper motor (PMSM).

2 is a block diagram for microstepping variable structure control of a permanent magnet step motor 100 according to an embodiment of the present invention as described above.

Hereinafter, a variable structure control method in the case of micro-stepping the permanent magnet step motor 100 according to an embodiment of the present invention with reference to the drawings will be described.

First, in order to move the position θ of the rotor 140 relative to the stator 130 to the desired position θ ^d of the rotor 140, the desired microstepping inputs are Can be defined as

Θ ^d in Equation (1) is the desired position of the rotor 140 with respect to the stator 130, V _a ^d and V _b ^d are the desired micro stepping of the permanent magnet step motor 100 in phase A and phase B, respectively. Voltage (desired microstepping voltage) to the desired voltage (desired voltage), R _a , R _b is the resistance value of the winding for the A phase and B phase, respectively. In addition, when the step motor 100 is controlled by the current, the desired currents i _a ^d and i _b ^d according to the desired micro stepping voltages V _a ^d and V _b ^d can be obtained by the following equation (2).

In the present invention, the controller is designed to ensure local exponential stability of the desired currents when the current is measured. To this end, the dynamics of the stepper motor 100 may be modified as in Equation 3 below.

In formula (3), d _a = [K _m ωsin (N _r θ)] / L, d _b = [K _m ω cos (N _r θ)] / L, respectively, and back-emf in phase )to be. K _m is a motor torque constant and N _r represents the number of teeth of the rotor 140.

In the present invention, a disturbance observer 220 is used to compensate for errors due to back EMF and phase delay, and the output of the disturbance observer 220 is controlled by a variable structure controller (VSC) for variable structure control (VSC). ). Here, the disturbance observer 220 is used to estimate the counter electromotive force, and the variable structure controller 210 is used for the exponential stability of the desired currents.

Referring to the process of designing the disturbance observer 220 is as follows. Equations (4) and (5) can be proposed to estimate d _a and d _b of Equation (3) above for counter electromotive force.

로 정의할 수 있다. 상기 식(5)의 양변을 2번씩 미분하면 다음 식(6)이 얻어진다.Here, the observation error of the counter electromotive force is

Can be defined as Differentiating both sides of the above formula (5) twice gives the following formula (6).

와

를 식(3)과 식(4)로 대체하면 다음 식(7)이 얻어진다.In the above formula (6)

Wow

Is replaced by equations (3) and (4), the following equation (7) is obtained.

From Equation (7), error transfer functions can be obtained as shown in Equation (8).

In Equation (8), s is a Laplace operator. Estimating a frequency response error (estimation error frequency response) from the formula it can be seen that the secondary high-pass filter ^{(2 nd order high pass filter)} .

The cutoff frequency of equation (8) is determined by the disturbance observer parameters k _p and k _l . In order to accurately estimate the back EMF, the cutoff frequency of the high band filter must be above the back EMF, that is, the frequency of d _i , N _r ω _max . ω _max is the maximum speed or maximum desired speed of the motor. The disturbance observer 220 of the control system 200 according to the present invention can accurately estimate the counter electromotive force.

FIG. 4 shows the frequency response of the transfer function between back EMF and estimation error when k _p and k _l are 2 × (0.707π × 1000) and (2π × 1000) ² . In addition, FIG. 5 shows estimation results for counter electromotive force when a sine signal is applied to a motor.

The method for controlling the microstepping variable structure of the permanent magnet step motor 100 using the disturbance observer 220 designed through the above process will be described.

With the desired position θ ^d of the rotor 140, a desired microstepping voltage V _a ^d , V _b ^d is generated. To generate an error voltage (V _a ^d i _a -R _a, V _b ^d -R _b i _b) in order to maintain the current in accordance with the desired micro-stepping voltage (V ^d _a, V _b ^d). The voltage error (V _a ^d -R _a i _a , V _b ^d -R _b i _b ) is the actual input current (i _a ) applied to the step motor 100 at the desired micro stepping voltage (V _a ^d , V _b ^d ). , i _b ) can be obtained from the difference of the product of the resistance R of the step motor winding.

In the counter-electromotive force voltage error using the (back-emf) estimated by using the disturbance observer (220) with (V _a ^d i _a -R _a, V _b ^d -R _{b b} i) and a variable structure controller with 210 Generates the actual input voltage (V _a , V _b ).

The variable structure control technique may be defined as in Equation (9) below.

이며 ρ_a와 ρ_b는 제어 입력 이득이다. 그리고 전압 오차는 e_a = V_a ^d-R_ai_a, e_b = V_b ^d-R_bi_b 이다. 식 (9)와 같이 설계가 되면 전압오차를 0으로 지수적으로 수렴시킬 수 있다. 만일 전류 제어일 경우 e_a와 e_b는 i_a ^d-i_a와 i_b ^d-i_b로 사용된다.In the above formula (9)

And ρ _a and ρ _b are the control input gains. And the voltage error is e _a = V _a ^d- R _a i _a , e _b = V _b ^d- R _b i _b . If the design is as shown in Eq. (9), the voltage error can be converged exponentially to zero. For current control, e _a and e _b are used as i _a ^d -i _a and i _b ^d -i _b .

The winding resistance values R _a and R _b of the step motors used in Equations (1), (2), (4), and (9) above are the motor data (that is, data on the performance or specifications of the motor provided by the motor manufacturer). It can be used as the same value provided in), and can be estimated and used through actual measurement or adaptive control.

The actual input voltage (V _a , V _b ) is input to the permanent magnet step motor 100 using a PWM (Pulse Width Modulation) driver.

The above description will be described once again with reference to FIG. 3. As shown in FIG. 3, the microstepping variable structure control method of the permanent magnet step motor 100 according to an exemplary embodiment of the present invention includes a permanent magnet step motor having a stator 130 and a rotor 140. In the microstepping variable structure control method of 100, a desired voltage V _a for driving the step motor 100 using a desired position θ ^d of the rotor 140 with respect to the stator 130. ^d , V _b ^d ) or obtaining _a desired current i _a ^d , i _b ^d 1100, the current according to the desired voltage V _a ^d , V _b ^d or the desired current i _a ^d , i _b ^d) to keep the error voltage (V _a ^d i _a -R _a, V _b ^d -R _b i _b), or step of using the current errors (i ^d -i _{a a, b} i ^d -i _b) to ( 1200), estimating a back-emf of the step motor using the disturbance observer 220 (1300), and the voltage error (V _a ^d -R _a i _a , V _b ^d -R _b i _b ) And the disturbance observer 220 For using the estimated back-EMF gibyeon structure controller 210, the actual input voltage (V _a, V _b), step 1400 and the actual input voltage (V _a, V _b) to get from the step motor 100 by And applying 1500.

As such, by using the disturbance observer 220 and the variable structure controller 210 for generating or estimating counter electromotive force, a microstepping variable structure control method for a permanent magnet step motor that simultaneously removes the counter electromotive force and phase delay can be provided. have.

The step 1200 of using the voltage error V _a ^d -R _a i _a , V _b ^d -R _b i _b includes the desired voltage V _a ^d , V _b ^d and the permanent magnet step motor 100. It can be obtained from the difference of the product of the input current (i _a , i _b ) of and the resistance (R) of the coil wound on the stator 130.

In the step 1300 of generating the counter electromotive force, the disturbance observer 220 may be in the form of a high pass filter. Referring to Equation (8) above, it can be seen that the disturbance observer 220 functions similar to the second order high-band filter. The disturbance observer 220 according to the present invention can accurately estimate the counter electromotive force if the cutoff frequency of the high band filter is higher than the maximum frequency of the counter electromotive force, that is, N _r ω _max .

Obtaining the actual input voltage (1400) is _a variable structure control of the voltage error (V _a ^d -R _a i _a , V _b ^d -R _b i _b ) and the back EMF by Equation (9) control). The variable structure controller 210 is used for this purpose, and desired phase current errors can be defined as sliding surfaces for the variable structure control (VSC). The variable structure controller 210 according to the present invention can improve the performance of the micro stepping by compensating the phase delay of the back EMF and the current without the position information.

The desired voltage _{^{(V a d, V b d}} ) or the desired current _{^{(i a d, i b d}} ) can be represented by the maximum voltage (V _max) or the sine wave function of the maximum current (I _max) (sinusoidal functions) have.

6 shows an experimental graph of position tracking errors according to the prior art and the present invention. Referring to FIG. 6, it can be seen that in the case of the present invention in a constant velocity period, the average of the tracking error is reduced to 60% of the prior art, which is an example of the variable structure control method of the present invention. This is because it ensures local exponential stability of the desired currents required for microstepping. That is, in FIG. 6, when the position tracking error is compared in a section of 0.5 seconds to 1.5 seconds, in which the speed is constant, the oscillation amplitude of the position tracking error is large in the case of the prior art, whereas in the case of the present invention, the position tracking error is large. It can be seen that the oscillation amplitude of the error is small.

On the other hand, in the acceleration and deceleration period, chattering appears due to VSC, but tracking error ripples are reduced and constant in a constant speed section.

As described above, the microstepping variable structure control method of the permanent magnet stepper motor according to the present invention uses a disturbance observer for estimating back EMF based on the variable structure control (VSC). Can be improved.

As described above, in one embodiment of the present invention has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention in the above embodiment The present invention is not limited thereto, and various modifications and variations can be made by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

100: permanent magnet step motor 110: case
120: axis of rotation 130: stator
140: rotor 200: variable structure control system
210: variable structure controller 220: disturbance observer
230: current PI controller

Claims (6)

In the microstepping variable structure control method of a permanent magnet step motor having a stator and a rotor,
Obtaining a desired voltage or a desired current for driving the stepper motor using a desired position of the rotor relative to the stator;
Using a voltage error or a current error to maintain a current according to the desired voltage or the desired current;
Estimating counter electromotive force of the step motor using the disturbance observer;
Obtaining an actual input voltage using the voltage error and the estimated back electromotive force; And
And applying the actual input voltage to the step motor; removing the back electromotive force and phase delay at the same time.
The method of claim 1,
Using the voltage error or current error,
Is obtained from the difference between the product of the desired voltage and the input current of the permanent magnet step motor and the resistance of the coil wound on the stator, or
The current error is obtained from the difference between the desired current and the input current of the permanent magnet step motor,
Microstepping Variable Structure Control Method of Permanent Magnet Step Motor.
The method of claim 2,
The disturbance observer in the step of estimating the back EMF microstepping variable structure control method of a permanent magnet step motor, characterized in that the filter.
The method of claim 3,
Obtaining the actual input voltage,
And a variable structure control of the voltage error and the estimated back electromotive force.
5. The method according to any one of claims 1 to 4,
The desired voltage or the desired current is a microstepping variable structure control method of a permanent magnet step motor, characterized in that expressed as a sine wave function of the maximum voltage or maximum current.
The method of claim 5,
The winding resistance value of the step motor is a microstepping variable structure control method for a permanent magnet step motor, characterized in that using the same value provided in the step motor data, or estimated through the actual measurement or adaptive control.

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